Here's a rebate free build with OS included. With this build, I went for a few things: Firstly, acoustics. If this thing is going right on top of your desk next to your head you'll want it to be quiet, and the Hyper 212 EVO does an excellent job at overclocking the G3258 quietly (I have it at 4.0GHz/1.25v and it's silent as a whisper at full load.)
Next up, acceptable performance. The G3258/750 Ti combo is one I've had personal experience with, and you will get very good performance in Source games, especially at those detail levels.
Second-to-lastly, it's well ventilated. One front intake, one rear exhaust and your CPU fan will keep air flowing nicely.
And finally, upgradeability - you could put an E3-1231v3 and a GTX 970 in this thing with no problem. Additionally, the GTX 750 Ti is a good card to upgrade from - you can slap it in basically any decent OEM computer for instant ascension.
PCPartPicker part list / Price breakdown by merchant
| Type | Item | Price |
|---|---|---|
| CPU | Intel Pentium G3258 3.2GHz Dual-Core Processor | $69.99 @ Amazon |
| CPU Cooler | Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler | $28.99 @ Amazon |
| Motherboard | ASRock H81M-ITX/WIFI Mini ITX LGA1150 Motherboard | $68.38 @ Newegg |
| Memory | Crucial Ballistix Sport 8GB (2 x 4GB) DDR3-1600 Memory | $41.49 @ Amazon |
| Storage | Samsung 850 EVO-Series 250GB 2.5" Solid State Drive | $95.25 @ Amazon |
| Storage | Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive | $49.39 @ Amazon |
| Video Card | EVGA GeForce GTX 750 Ti 2GB Superclocked Video Card | $142.98 @ Newegg |
| Case | BitFenix Prodigy (Black) Mini ITX Tower Case | $85.00 @ Amazon |
| Power Supply | SeaSonic G 550W 80+ Gold Certified Semi-Modular ATX Power Supply | $79.99 @ Amazon |
| Operating System | Microsoft Windows 7 Home Premium SP1 OEM (64-bit) | $102.98 @ Newegg |
| Prices include shipping, taxes, rebates, and discounts | ||
| Total | $764.44 | |
| Generated by PCPartPicker 2015-10-07 01:04 EDT-0400 |